The present invention relates to a medical imaging system for detecting faint fluorescence signals and in particular to a fluorescence imaging system usable in brightly lit environments, for example, in a surgical suite.
Fluorescent marker compounds that target cancerous tumors hold promise in allowing rapid identification of ex vitro tissue, for example, as obtained from a biopsy. The fluorescence signal developed by such marker compounds is relatively faint and normally viewed with special fluorescent microscopes that selectively illuminate the tissue with a proper exciting waveform and that include sensitive imaging systems that can isolate and detect the return fluorescence signal. Multiphoton and confocal microscope optics, for example, may be used to isolate the fluorescence signal from specific tissue while image intensifiers such as photomultiplier tubes or the like may be used to amplify the faint signal for detection.
While such fluorescent markers potentially simplify the identification of tumors, the ability of fluorescent markers to guide surgical procedure is limited by the time required to transport tissue samples to a remote location suitable for fluorescence analysis. Alternatively, the samples are imaged in the operating room, often before extraction from the patient. In this scenario, ambient illumination remains active but is dimmed and light filters are typically used and this limits the speed, sensitivity and applicability of the method due to the reduced signal and added background noise. Alternatively the ambient light needs to be switched off periodically during surgery, interrupting the workflow of the entire team.